It means he'll miss at least the game against the Parramatta Eels at Canberra Stadium on Saturday and reportedly be out for two months.

It's still unclear on whether he'll need surgery on a bulging disc in his neck.

Nicoll-Klokstad was caught awkwardly in an Isaah Yeo tackle in the 18th minute of the loss to the Penrith Panthers and was then caught high by a Viliame Kikau swinging arm three minutes later.

He was ruled out in the first half after failing his head injury assessment.

Nicoll-Klokstad's reportedly been ruled out for two months, although his visit to the specialist in the next week will determine exactly how long he'll miss.

Raiders coach Ricky Stuart named ex-Penrith custodian Caleb Aekins at fullback to make his Canberra debut.

"He's got further consultancy with our doc in regards to his neck problem," Stuart said.

"It's a little bit ongoing at the moment."

But in good news, co-captain Josh Hodgson (hip) has been cleared to face the Eels, while centre Curtis Scott was named after missing two games with broken ribs - although he faces a fitness test on Wednesday.

If he passes it then Sebastian Kris will drop to the extended bench, after the latter's impressive return to the NRL following a year off.

"There'll be a fitness test [on Wednesday for Scott]. It's been a bit of an odd week because we trained Monday, [Tuesday] they had massage and other bits inside," Stuart said.

"We didn't train on the field, we'll train on the field [on Wednesday]."

In another boost for the Green Machine, Parramatta five-eighth Dylan Brown will miss the game after taking the early guilty plea for a crusher tackle on Dragons lock Tyrell Fuimaono.

Eels coach Brad Arthur has named Will Smith to take his place alongside Mitchell Moses in the halves.

Stuart has opted to rest boom recruit Ryan James, allowing Emre Guler to come onto the Raiders bench.

James has been a revelation for the Green Machine this season since making the switch from the Gold Coast Titans.

But he's on the comeback from two knee reconstructions and Stuart wanted to manage his load after having a couple of head knocks in the past few games.

The 29-year-old's five games for the Raiders this season were his first in almost two years, having torn his anterior cruciate ligament in round six of 2019.

"I'm going to give him a week off. He hasn't had a lot of football over the last 18 months and he's hit the ground running and had a real good start to his time here with us," Stuart said.

"But he's had two head knocks over the last three weeks and I just feel as though a rest will help him.

"It's only early in the season and I don't want to ... take too much juice out of him."

Aekins was named in the No.1 jersey to come in for Nicoll-Klokstad.

He moved to the ACT on a one-year deal during the off-season in search of greater opportunity, having played 12 NRL games across three seasons for the Panthers.

Aekin's been named at fullback for all four of the Raiders' NSW Cup side this season.

He was brought to the capital to bolster the Raiders' depth in the outside backs.

Stuart also has the option to play wingers Jordan Rapana or Bailey Simonsson at the back.

"He's had some experience at fullback and it's a wonderful opportunity for him," he said.

"He brings utility value and he has played fullback before. He's been training there all off-season and playing there for us in our NSW Cup team so it's just a natural transition."

Guler has edged out Queensland State of Origin prop Dunamis Lui and New Zealand international Corey Harawira-Naera to play his first NRL game of the season.

Having missed most of the 2020 campaign due to an ankle injury, Guler's started the year in the second-tier NSW Cup - where he amassed 164 run metres against Penrith last week.

"Emre's coming in for Ryan James. Both him and Corey Horsburgh have been playing NSW Cup to try and get some match fitness and football back into their systems because they'd been out for so long last year," Stuart said.

"It's good for Emre to get that chance now."

NRL ROUND SIX

Saturday: Canberra Raiders v Parramatta Eels at Canberra Raiders, 7.35pm.

Raiders squad: 1. Caleb Aekins, 2. Bailey Simonsson, 3. Jarrod Croker (c), 4. Curtis Scott, 5. Jordan Rapana, 6. Jack Wighton, 7. George Williams, 8. Josh Papalii, 9. Josh Hodgson (c), 10. Sia Soliola, 11. Hudson Young, 12. Elliott Whitehead, 13. Joe Tapine. Interchange: 14. Tom Starling, 15. Ryan Sutton, 16. Siliva Havili, 17. Emre Guler. Reserves: 18. Sebastian Kris, 19. Matt Frawley, 20. Corey Harawira-Naera, 21. Dunamis Lui.

Eels squad: 1. Clinton Gutherson (c), 2. Maika Sivo, 3. Tom Opacic, 4. Marata Niukore, 5. Blake Ferguson, 6. Will Smith, 7. Mitchell Moses, 8. Reagan Campbell-Gillard, 9. Reed Mahoney, 10. Junior Paulo, 11. Shaun Lane, 12. Ryan Matterson, 13. Nathan Brown. Interchange: 14. Oregon Kaufusi, 15. Isaiah Papali'i, 16. Keegan Hipgrave, 17. Bryce Cartwright. Reserves: 18. Joey Lussick, 19. Haze Dunster, 20. Wiremu Greig, 21. Jordan Rankin.